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- Electrical thermography: safely inspecting switch cabinets | Testo
Electrical inspection with a thermal imaging camera:
Detect hotspots safely
Electrical thermography is particularly effective as a screening method: it quickly and contactlessly reveals temperature anomalies at connections, fuses or components – often while the system is operating. Results become meaningful when the load condition is appropriate, the target object is imaged large enough (IFOV) and measurements are documented in a standardized way (measurement points, scale, distance).
What does thermography do for electrical systems?
Thermography helps make hotspots and uneven temperature distributions visible and thereby prioritize potentially critical points. It is not a “cause measurement”, but provides indications: where is something unusual? For decisions (repair, retightening, replacement), the causes must subsequently be confirmed through suitable electrical tests and visual inspections.
Typical measurement objects in switch cabinets and electrical systems
Connections, terminals, fuses
Many anomalies occur at transitions: screw/spring terminals, busbar connections, fuses, contactors. These targets are often small – therefore distance/IFOV and focus are crucial.
Power electronics, motor feeders, drives
Power electronics, motor starters, variable frequency drive environments and drives are also inspected thermographically to identify uneven heating or unusual components.
Conditions: load, distance/IFOV and safety
Load condition: no hotspot without load
Many faults only become thermally apparent under a relevant load. Without load, a thermogram is often “too quiet” and may miss critical points. Therefore: document the load condition (as far as possible) and perform comparative measurements under similar conditions.
Distance/IFOV: imaging small targets correctly
Terminals and connections are often only a few millimetres in size. If they occupy only 1–2 pixels in the image, the pixel measures a mixed temperature of the connection and its surroundings. Practical rule: select the distance (or optics/resolution) so that the target is clearly larger than one pixel.
Safety and access: thermography without risk
Electrical inspections require safe working practices: sufficient distance, suitable access/coverings, clear responsibilities and compliance with operational safety rules. Thermography is advantageous because it works without contact – but it does not replace safe work organization.
Practical workflow: screening → prioritizing → verification
Screening: identifying anomalies
With clean focus and consistent scale logic, hotspots and uneven temperature distributions are identified. The goal is an “anomaly register”.
Prioritizing: comparing similar components
The comparison within similar components (e.g. several fuses/feeders) is often meaningful. This makes outliers visible without making blanket claims about absolute limit values.
Verifying: securing the cause
Verification follows thermography: visual inspection (e.g. corrosion, loose connection), electrical measurements (e.g. current, voltage, if necessary resistance measurement when shut down) and maintenance measures.
Documentation: establishing comparability and trends
For recurring inspections, standardization is the key: identical measurement points, clear naming, documented distance/viewing angle and the same scale logic. This makes it possible to identify trends (e.g. “hotspot increasing”) and prioritize measures.
Typical sources of error and countermeasures
Reflections on metals: consider ε/RTC and stabilize the viewing angle.
Excessive distance: check IFOV; move closer/use telephoto optics if necessary.
Scale changes: document scale values and keep comparative measurements consistent.
Out-of-focus image: actively check focus.
Next steps: guide, basics and instrument features
Deepen your practical knowledge with the guide, secure measurement parameters using the basics and check whether your camera resolution/optics and reporting workflow suit the task.
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